The lifeline of every building ventilation system is the exhaust system. The improper selection, application, installation, operation, and/or control of the exhaust gas system can cause poor system performance. This can lead to unsafe recirculation of fumes and exhaust gases, excessive noise, premature maintenance, fan failure, and wasted energy.
Conventional gas exhaust systems typically have a fan and a nozzle, or a fan and a stack device for pulling gas out of the interior of a building and then conveying the exhaust gas above the roof turbulence region. This may be accomplished by increasing the velocity of the exiting air in order to properly dispel the air or using a tall stack, both of which serve to avoid re-entrainment of the discharged exhaust gas.
In this regard, reference is made to U.S. Pat. No. 6,431,974, issued to Tetley et al., U.S. Pat. No. 4,806,076, issued to Andrews, and U.S. Pat. No. 5,439,349, issued to Kupferberg, which are designed to provide a high velocity jet for exhausting atmosphere and other gases. These exhaust fans are typically mounted on the roof areas of buildings and are used to carry exhaust gases as high as possible above the roof line of the building so as to ensure an effective final dilution of the gases within the greatest possible volume of ambient air and to ensure their dispersal over a large area with maximum dilution.
For example, the radial upblast exhaust fan apparatus described and shown in U.S. Pat. No. 4,806,076 has a nozzle in which two converging flow paths are defined by two respective passageways. A fan is positioned within the fan housing to urge exhaust gases to flow upwardly through the exhaust paths. A passive zone located between the two flow paths supplies environmental air for mixing by induction into the contaminated gases being exhausted through the converging flow paths.
These conventional systems exhaust the air away from building intakes or any other areas that could lead to re-entrainment of the discharged exhaust gas and to people inhaling the exhaust. The common range for velocity discharge from a stack is 1,000-3,000 fpm. The ANSI standard for these fans is to maintain 3000 fpm at the discharge of the fan.
Thus, in view of the foregoing, there is a need for control systems for exhaust gas fan systems that ensure proper system performance and provide efficient and safe operation. Embodiments of the present invention provide such control systems and methods.